126 



COMPARATIVE ANATOMY 



tremities, the anterior undergoing the most varied adaptative 

 modifications, and giving rise to tactile, prehensile, or flying organs 

 — or, as in aquatic Mammals, becoming once more converted into 



rowing organs. The limbs of all 

 the higher Vertebrata may, how- 

 ever, also be reduced to a single 

 ground-type. 



The fore- and hind-limbs show a 

 great similarity as regards the form 

 and position of their various parts. 

 A division into four principal sec- 

 tions can always be recognised : 

 in the case of the fore-limb these 

 are spoken of as upper arm (brach- 

 ium), fore-arm (antibrachium), wrist 

 (carpus), and hand (manus) ; and 

 in the hind-limb as thigh (femur), 

 shank (cms), ankle (tarsus), and 

 foot (pes) (Figs. 105, 106). The 

 bone of the upper arm (humerus) 

 and of the thigh (femur) is always 

 unpaired, but two bones are present 

 in the fore-arm and shank. The 

 former are called radius and ulna, 

 and the latter tibia and fibula. The 

 hand and foot are also respec- 

 tively divisible into two sections, a 

 proximal metacarjnis and metatarsus, 

 and a distal series of phalanges, 

 which form the skeleton of the 

 fingers and toes (digits). 



Both manus and pes are made 

 up of several series of cylindrical 

 bones. There are never more than 

 five complete series, which — except 

 as regards number— present essen- 

 tially similar primary relations 

 throughout the higher Vertebrates. 

 The skeleton of the carpus and 

 tarsus, each of which always consists 

 of a series of small cartilages or 

 bones, shows much variation; but the following may be taken 

 as a ground-type (Figs. 105 and 106). Round a centrale, which 

 may be double, is arranged a series of other elements, of 

 which three are proximal, and a varying number (four to six) 

 distal. The proximal, in correspondence with their relations 

 to the bones of the fore-arm and shank respectively, are spoken of 

 as radiale or tibiak, idnare or Jibulare, and intermedium ; while the 



Fig. 105. — Skeleton of the Right 

 Fore-arm, Carpus, and Hand 

 OF Sa/amandra maculosa. (From 

 above. ) 



B, radius ; U, ulna ; r, radiale ; i, 

 n, intermedio-ulnare ; c, cen- 

 trale ; 1 to 4, first to fourth 

 carpalia (according to Emery, 

 1 corresponds to the carpal of 

 the prepoUex, and 2 to the 

 common carpal of digits / and 

 //) ; Mr, Me, metacarpals ; 

 Ph, phalanges ; I to IV, first 

 to fourth fingers. 



